This study demonstrates a unique and crucial role of plasmacytoid dendritic cells (pDCs) and pDC-derived type I interferons (IFNs) in the pathogenesis of mouse coronavirus infection. pDCs controlled the fast replicating mouse hepatitis virus (MHV) through the immediate production of type I IFNs. Recognition of MHV by pDCs was mediated via TLR7 ensuring a swift IFN-alpha production following encounter with this cytopathic RNA virus. Furthermore, the particular type I IFN response pattern was not restricted to the murine coronavirus, but was also found in infection with the highly cytopathic human severe acute respiratory syndrome (SARS) coronavirus. Taken together, our results suggest that rapid production of type I IFNs by pDCs is essential for the control of potentially lethal coronavirus infections.

In this study, we analyzed the replication and budding sites of severe acute respiratory syndrome coronavirus (SARS-CoV) at early time points of infection. We detected cytoplasmic accumulations containing the viral nucleocapsid protein, viral RNA and the non-structural protein nsp3. Using EM techniques, we found that these putative viral replication sites were associated with characteristic membrane tubules and double membrane vesicles that most probably originated from ER cisternae. In addition to its presence at the replication sites, N also accumulated in the Golgi region and colocalized with the viral spike protein. Immuno-EM revealed that budding occurred at membranes of the ERGIC (ER-Golgi intermediate compartment) and the Golgi region as early as 3 h post infection, demonstrating that SARS-CoV replicates surprisingly fast. Our data suggest that SARS-CoV establishes replication complexes at ER-derived membranes. Later on, viral nucleocapsids have to be transported to the budding sites in the Golgi region where the viral glycoproteins accumulate and particle formation occurs.

Rift Valley fever virus (RVFV) is an important cause of epizootics and epidemics in

Severe acute respiratory syndrome (SARS) is caused by a novel coronavirus termed SARS-CoV. We and others have previously shown that the replication of SARS-CoV can be suppressed by exogenously added interferon (IFN), a cytokine which is normally synthesized by cells as a reaction to virus infection. Here, we demonstrate that SARS-CoV escapes IFN-mediated growth inhibition by preventing the induction of IFN-␤. In SARS-CoV-infected cells, no endogenous IFN-␤ transcripts and no IFN-␤ promoter activity were detected. Nevertheless, the transcription factor interferon regulatory factor 3 (IRF-3), which is essential for IFN-␤ promoter activity, was transported from the cytoplasm to the nucleus early after infection with SARS-CoV. However, at a later time point in infection, IRF-3 was again localized in the cytoplasm. By contrast, IRF-3 remained in the nucleus of cells infected with the IFN-inducing control virus Bunyamwera delNSs. Other signs of IRF-3 activation such as hyperphosphorylation, homodimer formation, and recruitment of the coactivator CREB-binding protein (CBP) were found late after infection with the control virus but not with SARS-CoV. Our data suggest that nuclear transport of IRF-3 is an immediate-early reaction to virus infection and may precede its hyperphosphorylation, homodimer formation, and binding to CBP. In order to escape activation of the IFN system, SARS-CoV appears to block a step after the early nuclear transport of IRF-3.

Rift Valley fever virus (RVFV) is responsible for large and recurrent outbreaks of acute febrile illness among humans and domesticated animals in Africa. It belongs to the family Bunyaviridae, genus Phlebovirus, and its negative-stranded RNA genome consists of three segments. Here, we report the establishment and characterization of two different systems to rescue the RVFV wild-type strain ZH548. The first system is based on the BHK-21 cell clone BSR-T7/5, which stably expresses T7 RNA polymerase (T7 pol). Rescue of wild-type RVFV was achieved with three T7 pol-driven cDNA plasmids representing the viral RNA segments in the antigenomic sense. The second system involves 293T cells transfected with three RNA pol I-driven plasmids for the viral segments and two RNA pol II-driven support plasmids to express the viral polymerase components L and N. It is known that the 59 triphosphate group of T7 pol transcripts strongly activates the antiviral interferon system via the intracellular RNA receptor RIG-I. Nonetheless, both the T7 pol and the pol I/II system were of similar efficiency. This was even true for the rescue of a RVFV mutant lacking the interferon antagonist nonstructural proteins. Further experiments demonstrated that the unresponsiveness of BHK-21 and BSR-T7/5 cells to T7 pol transcripts is most probably due to a deficiency in the RIG-I pathway. Our reverse genetics systems now enable us to manipulate the genome of RVFV and study its virulence mechanisms. Moreover, the finding that BHK-derived cell lines have a compromised RIG-I pathway may explain their suitability for propagating and rescuing a wide variety of viruses. INTRODUCTIONRift Valley fever virus (RVFV) is a serious pathogen affecting humans and livestock in sub-Saharan Africa, Egypt, Yemen and Saudi Arabia. Recurrent epidemics have killed thousands of animals, hundreds of humans, and caused significant economic losses (Balkhy & Memish, 2003). The severity of RVFV zoonosis as well as the capability to cause major epidemics have prompted authorities to list RVFV as a notifiable disease and a potential biological weapon (Borio et al., 2002).RVFV belongs to the genus Phlebovirus, family Bunyaviridae (Elliott, 1997). Bunyaviruses are enveloped and have a tri-segmented single-stranded RNA genome of negative or ambisense polarity, replicate in the cytoplasm, and bud into the Golgi apparatus. RVFV encodes five structural proteins: the viral polymerase on the large (L) segment, two glycoproteins (Gn and Gc) and the 78 kDa protein on the medium (M) segment, and the viral nucleocapsid protein (N) on the smallest (S) segment (Struthers et al., 1984). In addition, there are two nonstructural proteins, encoded on the M segment (termed NSm) and the S segment (termed NSs). These accessory proteins are dispensable for viral multiplication in cell culture (Gerrard et al., 2007;Vialat et al., 2000;Won et al., 2006), but play important roles for pathogenesis in vivo. In particular, the NSm and 78 kDa proteins were found to enhance intrahost viral spread , whereas NS...

In this study, infection of 293/ACE2 cells with severe acute respiratory syndrome coronavirus (SARS-CoV) activated several apoptosis-associated events, namely, cleavage of caspase-3, caspase-8, and poly(ADP-ribose) polymerase 1 (PARP), and chromatin condensation and the phosphorylation and hence inactivation of the eukaryotic translation initiation factor 2␣ (eIF2␣). In addition, two of the three cellular eIF2␣ kinases known to be virus induced, protein kinase R (PKR) and PKR-like endoplasmic reticulum kinase (PERK), were activated by SARS-CoV. The third kinase, general control nonderepressible-2 kinase (GCN2), was not activated, but late in infection the level of GCN2 protein was significantly reduced. Reverse transcription-PCR analyses revealed that the reduction of GCN2 protein was not due to decreased transcription or stability of GCN2 mRNA. The specific reduction of PKR protein expression by antisense peptide-conjugated phosphorodiamidate morpholino oligomers strongly reduced cleavage of PARP in infected cells. Surprisingly, the knockdown of PKR neither enhanced SARS-CoV replication nor abrogated SARS-CoV-induced eIF2␣ phosphorylation. Pretreatment of cells with beta interferon prior to SARS-CoV infection led to a significant decrease in PERK activation, eIF2␣ phosphorylation, and SARS-CoV replication. The various effects of beta interferon treatment were found to function independently on the expression of PKR. Our results show that SARS-CoV infection activates PKR and PERK, leading to sustained eIF2␣ phosphorylation. However, virus replication was not impaired by these events, suggesting that SARS-CoV possesses a mechanism to overcome the inhibitory effects of phosphorylated eIF2␣ on viral mRNA translation. Furthermore, our data suggest that viral activation of PKR can lead to apoptosis via a pathway that is independent of eIF2␣ phosphorylation.

Background:The current outbreak of SARS-CoV-2 has spread to almost every country with more than three million confirmed cases and over two hundred thousand deaths as of April 28, 2020. Rapid first-line testing protocols are needed for outbreak control and surveillance. Methods: We used computational and manual design to generate a suitable set of RT-RPA primer and exo-IQ probe sequences targeting the SARS-CoV-2 N gene. RT-RPA sensitivity was determined by amplification of in vitro transcribed RNA standards. Assay selectivity was demonstrated by means of a selectivity panel of 32 nucleic acid samples derived from common respiratory viruses. To validate the assay against full-length SARS-CoV-2 RNA, total viral RNA derived from cell culture supernatant and 19 nasopharyngeal swab samples (8 positive and 11 negative for SARS-CoV-2) were screened. All results were compared to established RT-qPCR assays. Results: The 95 % detection probability of the RT-RPA assay was determined to be 7.74 (95% CI: 2.87 -27.39) RNA copies per reaction. The assay showed no crossreactivity to any other screened coronaviruses as well as respiratory viruses of clinical significance. The developed RT-RPA assay produced 100% diagnostic sensitivity and specificity when compared to RT-qPCR (n=20). Conclusions: With a run time of 15 to 20 minutes and first results being available in under 7 minutes for high RNA concentrations, the reported assay constitutes one of the fastest nucleic acid based detection methods for SARS-CoV-2 to date and may provide a simple to use alternative to RT-qPCR for first-line screening at the point of need. Downloaded from https://academic.oup.com/clinchem/advance-article-abstract/doi/10.1093/clinchem/hvaa116/5834714 by guest on 09 June 2020

Severe acute respiratory syndrome (SARS) of humans is caused by a novel coronavirus of zoonotic origin termed SARS-associated coronavirus (SARS-CoV). The virus induces severe injury of lung tissue, as well as lymphopenia and destruction of the architecture of lymphatic tissue by as-yet-unknown mechanisms. In this study, the interaction of SARS-CoV with dendritic cells (DCs), the key regulators of immune responses, was analysed. Monocyte-derived DCs were infected with SARS-CoV and analysed for viability, surface-marker expression and alpha interferon (IFN-a) induction. SARS-CoV infection was monitored by quantitative RT-PCR, immunofluorescence analysis and recovery experiments. SARS-CoV infected both immature and mature DCs, although replication efficiency was low. Immature DCs were activated by SARS-CoV infection and by UV-inactivated SARS-CoV. Infected DCs were still viable on day 6 post-infection, but major histocompatibility complex class I upregulation was missing, indicating that DC function was impaired. Additionally, SARS-CoV infection induced a delayed activation of IFN-a expression. Therefore, it is concluded that SARS-CoV has the ability to circumvent both the innate and the adaptive immune systems.